Apparatus for testing cord fatigue



Sept. 30, 1952 T. J. RHODES APPARATUS FOR TESTING com) FATIGUE 3 Sheets-Sheet 1 Filed Dec. 11, 1947 INVENTOR.

H N D I T A T. J. RHODES APPARATUS FOR TESTING CORD FATIGUE Sept. 30, 1952 3 Sheets-Sheet 2 Filed Dec. 11, 1947 A TI'ORNBY T. 'J. RHeDEs APPARATUS FOR TESTING CORDFATIGUE Sept. 30, 1952 3 Sheets-Sheet 3 Filed Dec. 11, 1947 8M 6. WM

' Arromvzr Patented Sept. 30, 1952 UNITED STATES Pi s-TEN'I OFFICE v p 1 2,612,040 APPARATUS- FOR TESTING CORD FATIGUE. Thomas J. Rhodes, Ramsey, N. J. a'ssi'gnor. to United;.St ates' Rubber Company, New York;

N; Y., a corporation of New'Jersey Application- December 11, 1947, Serial No. 791.050

This invention. relates to. novel apparatus. for testing the. fatigue. properties of. a cord or. strand, and more particularly to the: testing of. a. tire cord' under. conditions. that. approximate the forces. that act. upon the cord. undertire runningconditions- It. is well known. that. the portion of. a pneumatic tire that ismost. likely to fail in normal use,v unless the tire is pierced. by a sharp object, lies in. that area- Wherethe side: walls. and tread meet. This is due to the fact thatv theco-rds lying.v in this. area are subjected. to an. axial compressing force. and. a. lateral compressingforce each time. the. treadin this. vicinity takes the.

load of the: wheell. This. axial compressing force apparently bends the individual fibers, as it is the portionv of. the cords that. are. subjected. to this axial, compression. as well as longitudinal.

' tension. that. undergoes. the greatest fatigue.

Stated; differently the principal fatigue forces acting on a tire cord. in. a running tire consist of axial tension,. axial compression, and lateral compression, the.- compression forces being produced by a. flattening. of the portion of the. tire that takes the load.

Attempts have been made. heretofore to test tire cords under. the several fatiguing forces that.

act upon-such cords in atire. Thishas been done by placing the cords to be tested in a body of vulcanized rubber and. then flexing the mass to produce the fatiguing forces; under which the cords are to be tested. This method of testing.

v i d ually to study the actionv of the same on the cord being tested.

The primary object of the present invention. is to. provide an apparatus for testing a cord}.

ireefrom a bonding rubber mass and under different. fatiguing forces. that can be independently changed as desired.

Ina-pneumatic tire for. vehicles the cords forming the tire carcass are subjected. to static. tension when the. tire is. inflated but not runningand to. dynamicforces. when. the tire is rolling along a roadway. Under. running condition the tire carcass is. subjected to reoccurring. cycles of different fatiguing forces that. occur. with each r0.- tation of the tire.

Asa selected portionof. the tire carcass rolls into positionto takethe loadof thevehicle wheel. thi'sportio-n willbe. flattened to some. extent by its contact with the road. The effect of this is a. tire cord under controlled fatigue producing foroeswhich closely approximate the fatigueproclucing. forces just mentioned thatacting upon a tire cord under tire running conditions. Such tests. consist. inv subjecting the cord repeatedly to a. dynamic longitudinal tension and then; to. acombined. lateral compressing andaxialicompressing force, and. continuing these fatigue producing forces until the cord parts. The. present methodand apparatus'may be used to test cord formed of. cotton, rayon, nylonor other. textile materials since eachtesting. forcemay be ad-' justed-asv required: for the material. being tested. The testing forces are.- preferably applied. to the cord at thev approximate speed at whichtheywould occur in a tire ontheroad; I

The above and other. features of the presentinvention will be further understoodfromthe;fols lowing description when. read. in connectionwith: the accompanying. drawings. illustrating. one. good practical embodiment; of the invention. and. wherein:

Fig. l is a front elevation of the testing-machine, the box which. houses the portion. of. the cord under test being shown. in section;

Eig. 2 is a horizontal sectional view talrenap proximately on the. line 2-2. of-Fi'g. l;

Fig. 3 on a larger scale is a. vertical'sectiona-l. view of apparatus. including, tensionedl strands. ready to be. twisted. into tight embracing relation with the tire cord.

Fig. 4 is a sectionalview takenon thelineK-d of Fig. 3. I

Fig. 5 is a view similar: to. Fig. 3 showing the:

tensioned surrounding. strands.twistedintostight v embracing relation-withthe-ti're cord- Fig. 6 is a sectional view. takenonlthe lines.6- 6 of'Fig. 5

Fig. 7 is a. more or less schematic view of. the:

essential parts. of. thetesting. apparatus shown. in

. Fig- 1.

Fig. is a larger view of the recording sheet having a plotted curve recorded by the testing apparatus of Fig. 1.

The apparatus of the present invention is designed to subject a cord repeatedly to different fatiguing forces and may be variously constructed. As shown in Fig. l of the drawing the various parts of the testing apparatus are supported by an upright casing or cabinet having the combined corner posts and legs [9, front wall I i and traversely extending bars i2.

. The cord C to be tested is threaded up through the apparatus which will be described so that it may be suspended in a vertical position from a supporting bracket I3 secured to the front wall of the cabinet and which bracket carries a cord clamp M under the control of the wing nut l5. Extending upwardly from the top of the cabinet is an upright post l6 which supports a grooved pulley I! about which the upper end portion of the cord C extends, and to the end of such cord is attached the weight 1 8. The purpose of this weight is to subject each cord C to be tested to the same amount of tension in threading up the testing machine.

The lower end of the cord C is firmly secured to a clamp i9 mounted on a rod which carries near its lower end a number of weights 2!, the number of these weights may be varied to vary the load upon the cord C. To the lower end of the rod 20 is attached the coiled spring 22 and the lower end of this spring is attached to an anchoring hook 23. The arrangement is such that this spring 22 continuously exerts a yielding downward pull upon the weighted rod 29 so that this rod may bounce under the resilient action of the cordC. The construction is such that the weighted rod .20 is repeatedly raised a short distance, by mechanism to be described, and then dropped to exert upon the cord C a dynamic longitudinal tension, and the amount of resiliency possessed by the cord will be shown by the degree of bounce it imparts to the weighted rod 20 immediately following the tensioning of the cord by the dropping weights.

As above pointed out a tire cord in a running tire is subjected not only to longitudinal tension but also to a lateral and axial compression. Mechanism for subjecting cord to these compressing forces will now be described. To this end in the construction shown the bracket [3 above described is provided with a laterally extending flange 24 in which is rotatably mounted an upright shaft 25. This shaft extends downwardly from the flange 24 and is provided at its lower end with a head 26 that extends into the air conditioning box 27 in which the cord is subjected to a plurality of fatiguing forces. The shaft 25 has a central opening longitudinally therethrough to clear the cord C being tested. A number of strands 28 are suspended from the shaft head 25 about the cord C, five strands being shown in the drawing. Each of these strands extends laterally inwardly through a hole in the head 26 as best shown in Fig. 3 and then downwardly in slightly spaced relation to the cord C, and each of these strands is attached to such head by a knot tied in the strand so that it will rest against the outer surface of the head 26. These strands 28 as shown in Fig. 3 extend downwardly in nearly parallel relation to each other to pass through a guide ring 29 such as a porcelain ring mounted within a support 30 attached to a bracket 3|.that is secured to the wall I]. These strands 28 extend from the ring 29 downwardly to the spreader disk 32 having its outer periphery notched to receive and equally space the strands 28. To the lower end of each strand 28 is rigidly secured by means of a clamping bolt 33 a weight supporting bracket 34 adapted to carry a plurality of weights 35. The arrangement is such that the strands 28 surrounding the cord C are maintained under uniformed tension by the weights 35. The spreader 32 is supported by the bracket 3| and this spreader has a central opening in which is mounted a trumpet 36 the upper end of which terminates adjacent the guide ring 29.

The purpose of the apparatus just described is to embrace tightly and contract longitudinally a short length of the cord C to subject the same to a lateral and axial compression, somewhat similar to that to which it is subjected in a tire when it lies at the juncture of the tire tread with a side wall of the tire. These compressive forces are repeatedly imparted to the enclosed length of cord by rotating the head 26 to thereby wind the strands 28 tightly about the cord C as shown in Fig. 5. After these strands 28 have been wound into snug engagement with the cord C, further twisting of these strands will serve to contract the cord they embrace and thereby subject the fibers forming the cord to a bending or buckling action that decreases the life of the cord. The strands 28 should be formed of strong highly flexible material in order to give good service.

During the operation of the testing machine of the present invention the cord is subjected repeatedly to a longitudinal tensioning force by the falling weights 2! and to a lateral and axial compressing force exerted by the strands 28, these forces being exerted successively and not simultaneously. The operating means for subjecting the cord to these forces comprises a power driven disk 31 which is rotatably supported by a shaft 37' mounted in bearings positioned upon two of the transverse bars 12. This disk is driven by an electric motor 38, belt 39, reducing pulleys 48, and second belt 4!. The rotating disk 3! is provided with several bolt holes spaced different distances from its central axis as shown in Fig. 1 and adapted to receive a bolt 62. The purpose of these bolt holes is to enable a cord anchoring head 43 to be connected to the disk 3'1 by the bolt 42 at a desired distance from the disk center, so that as the disk is rotated it will pull and relax the cables 44 and 45 attached to the head 43. These cables pass about a freely rotating pulley 46 and then the cable 45 passes downwardly about the guide pulleys M and 4B and its lower end is attached to a coiled spring 49. The lower end of this spring is attached to the weights 2| to raise these weights with a yielding action and then permit them to drop as the disk 31 is rotated. The arrangement is such that the cord C is free of tension while the weights are being raised by the cable 45. It will be noted that these weights are continuously urged downwardly by the coiled spring 22, the purpose of this spring 22 and the spring 49 being to permit the suspended weights 2! to vibrate or bounce in response to the elastic properties of the cord C.

The other cable 44 is provided to rotate the head 26 to wind the strands 28 tightly about the cord C as shown in Fig. 5 and then unwind these strands as shown in Fig. 3 to thereby repeatedly embrace and release the cord C. To this end the cable 44 is wrapped a number of 5. times'around-the'ishartfi and" isanchored .th'ereto at a desired pointbyca bolt or: th"e-'like-50:' The remaining portion of this cable" 44" extends around a" free" running: policy 51 and is attached to a coiled'springi52the 1ower"en'd"0f' which is. attached to an anchoring hook 53;

, When the cables 44' and 45 are in the position in which they are shown in Fig. 1 the cable: 45 will be free. from'the load exerted" by the" weights 21 as these weights are supported at this time by the cord' C; However it is not static load' of these weights that1exert'.a pro nounced' fatiguing. forceupon the cord Cbut rather thedynamic force exerted upon theco'rd".

exertiapull uponboth cables this will elevate the weights 2]. and rotate the head 26- so as to wrap. the strands. 28 tightly about" the cord C as shown in Fig. 5'. The. efiect of this is to slackofi the'tension of. the cord C! and to tightly embraceand. condense the cordaxially as above described. Itiwillthereiorebe seen thatas the disk..3T continuesetdrotate the. cord will be repeatedly subjected. to. a dynamic stretching actionandthen to. an. axial and lateral compressing. action to subject. the. cordto these different fatiguing forces, and. this testing. of. the cord! is. preferably. continued.- until. the cord. breaks=..

The number of revolutions made by the disk.

31 isconveniently recorded by providing the disk shaft 31 with a small eccentric 54 adapted to actuate a pivoted arm' 55' to thereby operate a switch within. the box 56 so as to control an electric circuit that operate the counter 51.

Since the recording device ETisoperated from the rotating: disk shaft 31 it isimportant to stop the machine as soon as the cord C breaks: Thisis accomplished in theconstruction". shown by-providing a lever 58 pivoted upon thecasing 59 that contains an electric switch. The? lever 58 is normally held elevated as shown in Fig: I by a blade: spring 60. The arrangement is such that when: the cord 0 breaks the clamp l 9 will move downwardly, and depress the lever 58 to cut'off the power to the electric-motor 38*.

It is desirable to control the. temperature and humidity within the box 21' throughout the cord testing operation, and to this end the box is provided with" a thermostat '1 and also with a small fan 62 mounted in the rear box 21' to force air into the front box and then out to the rear box through the openings shown. The rear box contains the heater 63. The cord 0, as above stated, extends from the clamping device l4 above the air conditioned box 21 downwardly to the clamping means l9 disposed below this box. The cord leaves the box through the tube 64. However only that portion of the cord C which is positioned in the upper portion of the box 2'! is subjected to the combined fatiguing forces. During a test the door of the box shown in Fig. 2 should be closed.

It is highly desirable to study the bouncing action of the weight rod at intervals during the cord testing operation as this gives an indication of the elastic properties of the cord and how these-'properties'vary from: time to time during the-testing: To this endkin the construction shown" mechanism is provided fonadvancing a recording" sheet of paper-"past the weights 2i.

This 'recording mechanism comprises a paper v guiding frame 65 having supported at one end thereof the-paperlet off roll '66- and at the other end thereof the papertake up roll 61 which may be rotated by theelectric motor I58 and belt 69. The'weight supporting rod 20- has associated with itsl'ower end; asbest' shown in Fig; 7, a marking pen 1o: The'arran'gement is such that when the motor-"68" is operated, during-theoperation of the 1 testing" machine; so as to advance the recording sheets, the rising and fallingmovement of the weight rod 20 will draw a curve on the'sheet S substantiallyas shown'in Figs. 1 and'lO. The

height 'of the curve is'not particularly important since this merely indicates the height to which the weight rod is liftedbythe cable45, but the important part ofthis curve is the lower portion thereoflying'between the points rand as, see Fig. 10. A stud'yof'the position marked :12 on the chart when readings are taken from time to timethroughout the cord testing operation will indicate the" cor'di growth or" elongation from the start to" thetimethecordbreahs; and the portion of the'curve"lyingrbetween'thepoint'zc and-m indicates" the resiliency or elasticityof thecord. Knowing thema'ss" of 'the-mov-mg weights 2 I and of the spring 2 2* it is possibleto calculate, by

means-of this chart; the maximum" stress-exerted on-thecordi Fig? Softhe-drawing-*showsdn full" Iines'across and to-a"quick'stronglongitudinal tension as the tirereturrrs' to they dotted line position of this view: Therowofarrows'inFig. 8.-show the downward direction in whichthe wheel load acts through the confined air and through the side walls of the tire:

Fig. yisa'sideview ofith'e' portions of'the tire ofFig: 8flyingnear theground G; the tread being" shown inxdotted'. lines-inthis' figure as not. distor-ted}. and" infulllines. asfia-ttened out. by the ground pressure and asdistorted from a true circle in; frontof andat the rear" of the flattened portion ofithe tire; A cord 0' is indicated in .Fig. 9' as lying; diagonally in the tire carcass. directly above the portion ofth'e tire which is flattened by its engagement with the ground. This is the area where these cords are subjected to both lateral and axial compression, due to the vertical downward force through the tire walls. This force is resolved into the component forces acting on the cord axially and at right angles to the cord as indicated by the arrows.

As the tire rotates in the direction indicated by the arrow in Fig. 9 along a road, the portion of the tire tread that is pulled away from the road by the wheel travel will be subjected to the peculiar wave movement indicated by W. This wave movement, which may be exaggerated somewhat by the showing of Fig. 9, subjects the tire cord to quick and severe longitudinal tension.

The cord testing mechanism of the present invention through the-falling weights 2! subjects the cord to fatiguing forces resembling those produced in the area marked W in Fig. 9, and the embracing strands 28 subject the cord to fatiguing forces resemblin those produced in the area marked T in Fig. 8.

A highly desirable feature of the present inven tion resides in the fact that an individual tire cord can be subjected to an axial tension, an axial compression, and a lateral compression, without the necessity of embedding the cord in a mass of vulcanized rubber, and also in the construction whereby the longitudinal tensioning force on the cord may be varied as desired independently of 1c cord compressing forces. This can be accomplished by varying the .number of Weights 21 provided upon the weight rod 29, and by varying the number of weights 35 carried by the weight support 35. Another highly desirable feature of the present invention resides in means for producing a dynamic force through the falling weights 2i that act upon the cord so that it can stretch and contract, as the weights rebound, in a damped harmonic cycle.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. A cord fatigue testing machine comprising, cord supporting means, mechanism for periodically subjecting the cord to a dynamic longitudinal tension, a plurality of longitudinally tensioned strands disposed about the cord, means for twisting these strands about the cord into and out of tight embracing relation therewith to periodically compress the cord laterally and axially, and power means for actuating said mechanism and said twisting means in rapidly reoccurring cycles.

2. A cord fatigue testing machine comprising, cord supporting means, mechanism for periodically subjecting the cord to a dynamic longitudinal tension, a plurality of longitudinally tensioned strands disposed aboutthe cord, means for twisting these strands about the cord into and out of tight embracing relation therewith to periodically compress the cord laterally and axially while it is free from said longitudinal tension, and power means for actuating said mechanism and said twisting means in rapidly reoccurring cycles.

3. A cord fatigue testing machine comprising, cord supporting means, mechanism for periodically subjecting the cord to a dynamic longitudinal tension, a plurality of longitudinally tensioned strands disposed about the cord, means for twisting these strands about the cord into and out of tight embracing relation therewith to periodically compress the cord laterally and axially, power means for actuating said mechanism and said twisting means in rapidly reocing surface a curve produced by the cords action under the testing conditions.

4. A cord fatigue testing machine comprising, cord supporting means, mechanism for periodioally subjecting the cord to a dynamic longitudinal tension, a plurality of longitudinally tensioned strands disposed about the cord, means for twisting these strands about the cord into and out of embracing relation with the cord to periodically compressthe cord laterally and axially, power means for actuating said mechanism and said twisting means in rapidly reoccurring cycles, and an air conditioned chamber surrounding the portion of the cord being tested.

5. A cord fatigue testing machine comprising, cord supporting means, mechanism for periodi-- cally subjecting the cord to a dynamic longitudinal tension, a plurality of longitudinally tensioned strands disposed about the cord, means for twisting these strands about the cord into and out of embracing relation with the cord to periodically compress the cord laterally and axially, power means for actuating said mechanism and said twisting means in rapidly reoccurring cycles, and means whereby the longitudinal tensioning force and axial compressing force may is independently varied.

5. A cord fatigue testing machine comprising. means for supporting a cord in a suspended condition, mechanism for subjecting the cord repeatedly to a dynamic stretching force including a weight and a weight suspending spring operable to raise the weight so as to relieve the cord from longitudinal strain and then drop the weight so that its fall will be arrested by its longitudinal pull upon the cord, and means for automatically recording the movement of the weight.

THOMAS J. RHODES.

REFERENCES CITED The following references are of record. in the this patent:

' UNITED STATES PATENTS Number Name Date 1,156,726 Upton et al Oct. 12, 1915 1,499,546 Oxley July 1, 1924 1,635,787 Hort July 12, 192'? 1,739,298 Ford Dec. 10, 1929 1,885,209 Koester Nov. 1, 1932 1,960,675 Koester May 29, 1934 2,157,092 Allen et al. May 9, 1939 2,265,142 Burke et al Dec. 9, 1941 FOREIGN PATENTS Number Country Date 411,124 Germany Mar. 16, 1925 

